1. Field of the Invention
The present invention relates to light-emitting elements which emit light by current excitation, and light-emitting devices and electronic devices using the same.
2. Description of the Related Art
In EL displays which have been commercialized recently, images are displayed by changing and combining luminance, emission time or the like of red (R), green (G) and blue (B) luminescences. R, G and B luminescences can each be obtained by driving a light-emitting element in which a light-emitting layer is formed between a pair of electrodes. In such light-emitting elements, at least one of the electrodes is formed of a transparent conductive film such as ITO (indium tin oxide) so that visible light can pass therethrough.
In such light-emitting elements, when a distance between a light-emitting layer and an electrode through which light passes is not suitable (in other words, an optical path length is not controlled suitably), colors are changed strangely or an extraction efficiency of luminescence decreases. In order to solve such problems, a technique shown in Reference 1 has been proposed, for example (Reference 1: Japanese Patent Application Laid-Open No. 2001-102175).
Forming a metal doping layer to be in contact with a cathode as described in Reference 1 is thought to be effective. However, a problem remains with the technique as described in Reference 1 in that a distance between a light-emitting layer and an anode cannot be adjusted. In addition, a metal such as Mg or Li as described in Reference 1 can be a cause of reduction of a light-transmitting property.